Die module for a crosshead extrusion system

ABSTRACT

An extrusion system for extruding a layer of a plastic or rubber material onto a work piece without having to continuously adjust the extrusion system during the “set-up” mode to “full-run” mode, wherein the extruded layer exhibits a predetermined cross-section size and a uniform wall gauge concentricity.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to an extrusion system containing afixed center die module which requires no mechanical adjustments, forcontinuously extruding a molten material or a formable mass to provide atubular structure having a predetermined cross-section size and auniform wall gauge concentricity. More particularly, the presentinvention relates to a crosshead extrusion system.

[0002] Hoses made primarily of polymeric materials are widely used fortransporting various fluids such as water, gasoline, coolants, powersteering fluids, transmission fluids, etc. Typically, these hoses areused in automobiles, trucks, buses, aircraft, locomotives and watercraft to transmit such fluids. Generally, for such applications it isnecessary to provide high pressure hoses having multiple layers,including reinforcing layers, in order for the hoses to withstand thepressures and temperatures involved, and to meet the various federal andstate emission regulations, and still exhibit dimensional stability andrugged durability required for today's fuel powered internal combustionengines. For example, U.S. Pat. No. 4,330,017 to Satoh describes anautomobile fuel hose comprising a two-ply rubber tube covered with areinforcing fiber layer and further with a protective rubber layer. Thehose is constructed from a very thin inner layer of afluorine-containing rubber which is resistant to fuel, and an outerlayer of a synthetic rubber such as epichlorine rubber orethylene-acrylic rubber which is less resistant to gasoline, but issuperior in cold resistance. The extrusion system of the presentinvention can be used in the manufacture of any polymeric hose, e, g,garden hoses, air pressure hoses, and industrial hoses such as thoseused in connection with hydraulic presses and the like.

[0003] U.S. Pat. No. 5,566,720 to Cheney et al. proposes a multiplelayer hose comprising a first layer made up of a melt processiblefluoroplastic terpolymer wherein the innermost surface is capable ofprolonged exposure to hydrocarbon-containing fluids, and a second layercomposed of a resinous thermoplastic material such as polyamide which isbonded directly to the outwardly oriented surface of the first layer.

[0004] U.S. Pat. No. 5,524,673 to Noone et al. describes an elongatedtubing which includes a first layer of an extrudable, melt-processiblethermoplastic material, and a second layer of an extrudable,melt-processible thermoplastic material wherein the second layer iscapable of sufficiently permanent laminar adhesion with the first layerto prevent delamination during the desired lifetime of the tubing. Atleast one of the first and second layers is resistant to permeation ofhydrocarbons. In addition to the first and second layers, the tubingincludes a third layer adhered to the second layer.

[0005] Typically, multi-layer tubular structures are manufactured usingextrusion processes and, more particularly, using crosshead extrusionprocesses as described in U.S. Pat. No. 4,361,455 to Arterburn. Suchcrosshead extrusion systems are employed not only in the manufacture ofrubber tubes and hoses, but also for coating cylindrical work pieceswith highly viscous materials such as unvulcanized rubber as describedin U.S. Pat. No. 4,832,588 to Rasmussen, and in the manufacture ofcoated wire and cables as described in U.S. Pat. Nos. 5,183,669;5,780,066; 5,882,694; and 5,980,226 all to Guillemette; and U.S. Pat.No. 5,830,516 to McAlpine et al.

[0006] Typically, in the manufacture of rubber tubing or rubber-coatedwire, the molten rubber material is extruded by means of a crossheadextrusion system which receives a stream of molten rubber material andcauses the molten rubber material to be distributed around thecircumference of a wire or tube. In the present invention, the termmolten is used to define a formable mass and is not intended tospecifically suggest that the formable rubber material is in a molten orliquid state. A variety of crosshead devices have heretofore been knownin the art for manufacturing hoses and for applying rubber coatingsaround the circumference of a wire or tubular member. Furthermore, it isknown in the art to simultaneously extrude more than one layer of moltenrubber to provide a multi-layer tube. Such a process is accomplished bymeans of multi-layer crosshead extruder devices such as that describedin U.S. Pat. No. 4,798,526 to Briggs et al. Such devices typicallyutilize two or more crosshead extruders for co-extrusion of multiplelayers.

[0007] It is also known in the art that it is extremely difficult toestablish an even and balanced flow of molten material around thecircumference of a wire, mandrel or tube. For example, it is known thatconventional crosshead extrusion methods pose several inherent problemssuch as lengthy “set-up” time which is the time spent adjusting theextruder for a desired circumferential size and uniform wall gaugeconcentricity. After the adjustments are made and remade several timesand the “set-up” is finally complete, the material being extruded from“set-up” mode to “full run” mode has, typically, become hotter on theinside, or extrude side, of the crosshead, thus causing concentricity ofthe tubular structure to be comprised. In addition, the overheatedplastic or rubber material frequently becomes discolored and exhibitsother undesirable characteristics . . . Furthermore, it is known thatsplitting and reblending of the molten material can cause the moltenmaterial to blend together unevenly forming undesirable weld or jointlines in the finished product. Accordingly, there is a need for anextrusion system which overcomes the inadequacies and undesirablecharacteristics of the prior art extrusion systems.

SUMMARY OF THE INVENTION

[0008] The present invention provides a new and improved crossheadextrusion system wherein the crosshead extruder housing is designed toaccept a fixed center or non-adjustable die module which is capable ofbalancing the flow of molten material to the die and maintaining thisbalance from a “set-up” mode to a “full-run” mode. Die modules areknown, however, such die modules are notorious for requiring continuousadjustment of the die module in the housing in order to provide hoseshaving acceptable cross-section size with a uniform wall gaugeconcentricity. It has now been found that a tubular member having apredetermined cross-section size and a uniform wall gauge concentricitycan be extruded in an extrusion system, particularly, a crossheadextrusion system which employs the die module or torpedo of the presentinvention. The die module of the present invention has a fixed centerand requires no mechanical adjustments while providing a balanced flowof molten or formable material to the die and maintains this balancefrom a “set-up” mode to a “fill-run” mode. The tubular member formedusing the extrusion system of the present invention has a predeterminedcross-section size and a uniform wall gauge concentricity.

[0009] A critical feature of the new crosshead extrusion system is theconstruction of a fixed center die module or “torpedo” which residesinside the extruder housing. The torpedo is designed to split the moltenmaterial coming from the screw into two substantially equal parts orcontrolled flow, and then split each of these two parts into two moresubstantially equal parts, thereby providing four substantially equalparts or controlled flow, thus allowing for a balanced volume flow tothe die. Another feature of the crosshead extrusion system is theoutside part or the body of the crosshead extruder which is designed toaccept “non adjustable” dies. Also the extruder is designed with dualcontrollable temperature zones in the front of the crosshead body tocontrol the temperature of the material flowing through the body of theextruder.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a cross-sectional view of the crosshead extrusion systemof the present invention;

[0011]FIG. 2 is a perspective view of the fixed center die module of thepresent invention;

[0012]FIG. 3 is a front view of the die module of the present invention;

[0013]FIG. 4 is a right side view of the die module of the presentinvention;

[0014]FIG. 5 is a left side view of the die module of the presentinvention;

[0015]FIG. 6 is a bottom view of the die module of the presentinvention;

[0016]FIG. 7 is a cross-sectional view of the die module taken alongline 7-7 of FIG. 6;

[0017]FIG. 8 is a top view of the die module of the present invention;and

[0018]FIG. 9 is a cross-sectional view of the die module taken alongline 9-9 of FIG. 8.

DETAILED DESCRIPTION OF THE INVENTION

[0019] Turning to the drawings, FIG. 1 illustrates a cross-sectionalextrusion system of the present invention. The extrusion system 10comprises a housing 12 having a tapered interior wall surface 14, thecircumference of the interior wall surface being smaller in the front ofthe housing 12 than in the rear of the housing. The housing 12 isadapted with a threaded surface 28 at the front of the housing 12 tothreadedly secure a die head (not shown) to the housing 12. As shown inFIG. 1, an extrusion module 18 is placed in the interior of the housing12 such that the frusto-conical exterior surfaces 22 of the module 12mates with the tapered interior wall surface 14 of the housing 12. Theextrusion module 12 has a tubular bore 32 with a uniform circumferenceextending through module 12 for transporting a wire, mandrel, or tube(not shown) in accordance with the present invention. The module 18 issecured in the housing 12 using a nut (not shown) which is threadedlylocked onto the housing 12 using threaded surface 26.

[0020] Molten material such as plastic and/or vulcanized or unvulcanizedrubber is delivered under high pressure and temperature to the interiorof the housing 12 through conduit 40. The pressure and temperatureemployed are those typically used in conventional extrusion systems forsimilar material plastic or rubber materials. The molten material isdistributed by diverter 38 in the fixed center die module throughchannels 42 between raised surfaces 24 to uniformly divide the moltenmaterial into two substantially equal parts or equal flow. The moltenmaterial continues to be distributed forward through the channels 44wherein the two equal parts or flow of molten material are eventuallyuniformly divided into four equal parts of molten material. Finally, themolten is directed to tubular bore 32 where, in one aspect of theinvention, it is evenly distributed and coated onto a cylindrical bodysuch as a hose, a wire or a mandrel, to provide a tubular structure ofmolten material having a predetermined cross-section and uniform wallgauge concentricity. In another aspect of the invention, the moltenmaterial may be employed to provide an unsupported hose. In a preferredaspect of the invention, one or more temperature controlling zones 20are employed in the housing 12 to aid in controlling the wall gaugeconcentricity of the extruded material. Most preferably, the housing 12is constructed with dual temperature controlling zones, and thetemperature of the temperature controlling medium is monitored andcontrolled to assure of proper temperature.

[0021] The extrusion system of the present invention can be employed ina conventional extrusion system for the extrusion of a single ormultiple layer hose using a mandrel to configure the interiorcircumference of the hose, or the extrusion system can be used in across-head extrusion system to coat wire or cable in anextrusion/coating operation. The present extrusion system also can beemployed to provide an unsupported tube. The extrusion system of thepresent invention has been found to be particularly useful in extrudinga layer of vulcanized or unvulcanized rubber material on a mandrelemploying a cross-head extruder. The hose is then reinforced with areinforcing layer such as braided fiber e.g. glass fiber, polyesterfiber, polyamide fiber, partially acetyl-formed polyvinyl alcohol fiberor the like to form a high pressure hose such as that used as a powersteering hose in the automotive industry.

[0022] While the extrusion system of the present invention is shown anddescribed herein certain specific structure, it will be obvious to thoseskilled in the art that certain modifications may be made withoutdeparting from the spirit and scope of the invention concept asindicated by the scope of the appended claims.

What is claimed is:
 1. An extrusion system for continuously extrudingmolten material to form a tubular structure having a predeterminedcross-section size and uniform wall gauge concentricity, said apparatuscomprising an extrusion housing having a tapered interior wall surface;an extruder die head releasably connected to said housing; anintroduction port in said housing for introducing said molten materialinto the interior of said housing; a fixed center die module configuredto slidably mate with the tapered interior wall surface of said housing;and means for securing said fixed center die module in said housing. 2.The extrusion apparatus of claim 1, wherein said housing furthercomprises at least one controllable temperature zone.
 3. The extrusionapparatus of claim 1 wherein said housing comprises dual controllabletemperature zones in the front part of the housing.
 4. The extrusionapparatus of claim 1, wherein said fixed center die module is configuredsuch that molten material introduced into said housing is divided intofour parts providing balanced flow of said molten material to saidextruder die head.
 5. The extrusion apparatus of claim 1, wherein saidfixed center die module comprises a tubular member having a uniforminner circumference along its longitudinal axis and a plurality ofraised surfaces extending from and integral with the outer circumferenceof said tubular member, said plurality of raised surfaces exhibiting afrusto-conical configuration along said longitudinal axis and providinga plurality of passages between said plurality of raised surfaces suchthat said molten material is divided into equal parts during extrusion.6. The extrusion apparatus of claim 5, wherein said fixed center diemodule is configured such that molten material is divided into two equalparts and the two equal parts are subsequently divided into four equalparts.
 7. The extrusion apparatus of claim 1, wherein said apparatus isa crosshead extrusion apparatus.
 8. The extrusion apparatus of claim 1,wherein said tubular structure is useful as a high pressure hose.
 9. Theextrusion apparatus of claim 8, wherein said tubular structure is usefulas a power steering hose.
 10. The extrusion apparatus of claim 9,wherein said tubular structure is covered with a reinforcing layer. 11.The extrusion apparatus of claim 10, wherein said reinforcing layer isbraided or spiral constructed fiber.
 12. The extrusion apparatus ofclaim 11, wherein said braided or spiral constructed fabric is selectedfrom the group consisting of glass fiber, polyester fiber, polyamidefiber and partially acetyl-formed polyvinyl alcohol fiber.
 13. Theextrusion apparatus of claim 1, wherein said molten material isvulcanized or unvulcanized rubber.
 14. The extrusion apparatus of claim1, wherein the configuration of said fixed center die module precludesthe need for continuous die adjustment to achieve predeterminedcross-section and uniform wall gauge of said extruded tubular structure.15. A fixed center die module for use in an extrusion apparatus whereinmolten material is continuously extruded to form a tubular structure,said fixed center die module comprising a tubular member having auniform inner circumference along its longitudinal axis and a pluralityof raised surfaces extending from and integral with the outercircumference of said tubular member, said plurality of raised surfaceexhibiting a frusto-conical configuration along said longitudinal axisand providing a plurality of passages between said plurality of raisedsurfaces such that said molten material is divided into equal partsduring extrusion.
 16. The fixed center die module of claim 15, whereinsaid molten material is divided into two equal parts and the two equalparts are subsequently divided into four equal parts providing balancedflow of said molten material to an extrusion die head.
 17. The fixedcenter die module of claim 15, wherein said module is useful inextruding a tubular structure having a predetermined cross-section sizeand uniform wall gauge concentricity.
 18. The fixed center die module ofclaim 15 wherein the configuration of said module precludes the need forcontinuous die adjustment to achieve predetermined cross-section sizeand uniform wall gauge of said extruded tubular structure.
 19. In anextrusion apparatus for continuously extruding molten plastic or rubbermaterial to form a tubular structure comprising an extrusion housing andan extrusion die assembly, the improvement comprising employing in theinterior of said extrusion housing, a fixed center die module comprisinga tubular member having a uniform inner circumference along itslongitudinal axis and a plurality of raised surfaces extending from andintegral with the outer circumference of said tubular member, saidplurality of raised surfaces exhibiting a frusto-conical configurationalong said longitudinal axis and providing a plurality of passagesbetween said plurality of raised surfaces such that said molten materialis divided into two equal parts and the two equal parts are subsequentlydivided into four equal parts providing balanced flow of said moltenmaterial to an extrusion die head to form a tubular structure having apredetermined cross-section and uniform wall gauge concentricity,wherein the configuration of said fixed center die module precludes theneed for continuous die adjustment to achieve predeterminedcross-section size and uniform wall gauge of said extruded tubularstructure.